1. Field of the Invention
The present invention relates to apparatus for making up and breaking out tubular connections. Particularly, the present invention relates to a gripping system for an apparatus for making and breaking tubular connections. The present invention also relates to a locking apparatus for a rotary.
2. Description of the Related Art
Oilfield tubulars such as drill pipe and casing are employed in sections which are joined together at their ends by threaded connections. Typically, power tools are used to couple (“make up”) or decouple (“break out”) threaded connections. Power tools such as tong assemblies have been developed to threadably secure tubulars together.
A tong assembly generally includes a power tong and a backup tong. The power tong is associated with a power drive to grip and apply torque to a first tubular to cause it to rotate. The backup tong is adapted to grip second tubular during engagement between the tubulars. The backup tong typically maintains the second tubular in a stationary position, thereby allowing relative rotation between the first and second tubulars. The backup tong may also allow some radial or axial displacement between the tubulars to accommodate deviations between the shapes of the tubulars during makeup.
The power tools generally used to connect tubulars are adapted and designed to provide the appropriate torque to achieve proper threaded connection. The threads may become damaged or stripped when excessive force is applied. Typically, the power tongs are provided with torque gauges to prevent damage to the threads. In many arrangements, hydraulic power is used to operate the power tool.
Many different gripping systems are known to be used for a tong. In one example, the tong may only have one powered jaw. In this system, the “active” jaw is a cam driven master jaw and the remaining “passive” jaws react to the forces of the active jaw. In some instances, the passive jaws may only react 50% of the gripping force applied by the active jaw, as illustrated in FIG. 1. In this situation, the load will not be equally displaced between the jaws, e.g., the active jaw supplies 10 ton, while each of the passive jaws only react 5 tons.
In order to make up or break out a connection between tubulars in a tubular string, torque must be supplied over a large angle without having to take time to release and clamp the tubular again. For some jaw assemblies, the torque of the rotor enters the active jaw through a roller disposed at the back of the active jaw. When a small diameter tubular is handled, the active jaw may swivel to cause the gripping force to offset, thereby by damaging the pipe surface. It is also known that when used at high torques, some jaw assemblies tend to tilt and provide a non-uniform load on the tubular surfaces. When the jaw assembly tilts, only a portion of the jaw assembly contacts the tubular, thereby causing damage to the tubular, limiting the torque that can be applied, and causing failure of the jaw assembly itself.
There is a need, therefore, for a gripping system having a passive jaw adapted to transmit a reactive force that is equivalent to the gripping force applied by the active jaw. There is also a need for an improved gripping system for transferring torque to the tubular. There is a further need to prevent rotation of the rotary when it is open.